1. Field of the Invention
This invention relates to current collectors and more particularly to a multilayered structure for use as a current collector in a battery.
2. Description of Related Art
A typical battery structure includes two electrodes, serving as the anode and cathode, in contact with an electrolyte. Originally the anode and cathode served also as the conduit through which the electric current generated by the battery was guided to a point outside the battery for eventual use, and the anode and cathode served the dual function of electrode and current collector.
As battery technology became more sophisticated, the current collection function was in a number of applications done through a separate conductor which did not necessarily function as an electrode. The term "current collector" as used in this application is understood to mean the combination of the elements that function as anode or cathode, generically known as electrodes, together with the elements for collecting or distributing the current accumulated on the electrodes, be it a signal current or current generated in a battery.
When the current collector comprises a metal or metalized support in addition to the electrode material, it is important that the anode or cathode electrode material exhibit good contact and adhesion to the metal as such good contact and adhesion improve the overall efficiency and life of the battery. It is known to use a coating between the electrode material and the metal to enhance the contact and/or adhesion of the electrode material to the metal and to protect the metal from the often corrosive effects of the electrolyte and in certain cases of the anodic or cathodic material itself. Further more such protective coating at times serves to prevent the support metal from becoming part of the electrochemistry of the battery.
U.S. Pat. No. 4,173,066 issued to Kinsman discloses a current collector comprised of an aluminum foil coated with a thin layer of a conductive primer; two plies of a vinyl film are laminated over the primed side of the aluminum foil. Both the primer and the vinyl film are rendered conductive through the use of carbon black incorporated therein. The cathode and anode electrode materials are adhered to the vinyl film.
While this current collector works well in a LeClanche type cell, it dissolves in many organic solvents found in certain modern battery cells particularly Lithium based batteries which have electrolytes containing propylene carbonate or other ethers that swell and dissolve the vinyl film. The problem is aggravated in lithium batteries which often operate at elevated temperatures, i.e. 60.degree. C. and higher; the higher temperature tends to accelerate the swelling and dissolution processes.
There is, thus, still a need for a primer layer that improves adhesion of the electrode to the metal support surface and which is strongly resistant to organic solvents used in modern battery cells, particularly in lithium cells, while still providing good conductivity.